And some of that money may well be wending its way into politicians' election coffers through the generous campaign contributions those lobbyists routinely make to buy access and reward friends.

"There's pretty clear evidence that foreign money is being used, at least indirectly, to finance U.S. elections," says Benjamin J. Freeman, a post-doctoral fellow at the Project on Government Oversight, a nonprofit advocacy group that focuses on investigating waste, fraud and abuse in the federal government.

As part of the research for his book about foreign lobbying, "The Foreign Policy Auction," slated for publication in late 2011 or early 2012, Freeman says he has documented "dozens of instances where lobbyists meet with representatives to advocate for foreign clients, and then give the exact same representative a campaign contribution that very same day."

"These folks can't give directly, so what you're finding is these firms want to represent the interest of their clients the best they can," explains Jon Pevehouse, a political science professor at the University of Wisconsin who is in the process of creating a foreign lobbying database for his research.

Pevehouse estimates that foreign interests spent about $200 million on lobbying in 2008, the most recent year for which he has data. He has not yet calculated how much the lobbyists hired by those interests then turned around and gave to political campaigns.

But at the very least, campaign finance experts say, foreign interests are doing what a lot of other groups in Washington are doing: buying influence.

"Our influence system works with lobbyists using campaign contributions as a means of obtaining access and influence for their clients — and the lobbying system in this country is available to anyone," says Fred Werthheimer, who runs Democracy 21, a group that promotes and defends campaign finance laws. "What foreign interests have learned is if they want to try to obtain influence in Washington, they ought to do it the same way that corporations do it."

"Generally speaking, what they are trying to do when they hire these lobbyists who make these contributions is get the access," says Bill Allison, editorial director of the pro-transparency Sunlight Foundation.

But foreign lobbying is distinct from domestic lobbying because of the possible divergence with U.S. interests. "If you're cynical," says Pevehouse, "then you think this stuff is dangerous, because it's really distracting Congress from what it should be doing in foreign affairs."

And while federal candidates are allowed to accept campaign donations from American citizens — even lobbyists — as long as there is no explicit quid pro quo, when it comes to foreign nationals, it's a different story entirely.